package queue;

public class LoopQueue<E> implements Queue<E> {

    private E[] data;
    private int front;  //队首所在索引
    private int tail;   //下一个元素所在的索引
    private int size;   //

    public LoopQueue(int capacity){
        data = (E[]) new Object[capacity + 1];
        front = 0;
        tail = 0;
        size = 0;
    }

    private LoopQueue(){
        this(10);
    }

    public int getCapacity(){
        return data.length - 1;
    }


    //入队
    @Override
    public void enqueue(E e) {
        //step1：判断队列是否满了
        if((tail+1) % data.length == front){
            //队列满了
            resize(getCapacity() * 2);
        }
        data[tail]  = e;
        tail = (tail + 1) % data.length;
        size++;
    }

    //出队
    @Override
    public E dequeue() {
        if(isEmpty()){
            //
        }

        E ret = data[front];
        data[front] = null;
        front = (front + 1) % data.length;
        size--;

        if(size == getCapacity() / 4 && getCapacity() / 2 != 0){
            //执行缩容操作
            resize(getCapacity()/2);

        }
        return ret;
    }


    //获取队首元素
    @Override
    public E getFront() {
        if(isEmpty()){
            throw new IllegalArgumentException();
        }
        return data[front];
    }

    @Override
    public int getSize() {
        return size;
    }

    @Override
    public boolean isEmpty() {
        return front == tail;
    }

    private void resize(int newCapacity){
        E[] newData = (E[]) new Object[newCapacity + 1];
        for(int i = 0 ; i < size ; i++){
            newData[i] = data[(i + front) % data.length];
        }
        data = newData;
        front = 0 ;
        tail = size;

    }
}
